1. Field
Example embodiments relate to a printed circuit board on which a semiconductor package is mounted and a method for mounting a semiconductor package using the printed circuit board. Other example embodiments relate to a printed circuit board with a semiconductor package having leads as external connection terminals and a method for mounting a semiconductor package using the printed circuit board.
2. Description of the Related Art
In the semiconductor packaging field, there have been a number of changes in the semiconductor packaging process and the materials used to satisfy customers' demand for environmentally-friendly products. As a representative example, a lead (Pb) component has been removed from solder in many semiconductor packages. The removal of the lead component may have caused unexpected defects to occur in the assembly process of semiconductor packages. Semiconductor packages having leads for external connection terminals, for example, a small outline package (SOP), a thin small outline package (TSOP), a quad flat package (QFP) and/or a thin quad flat package (TQFP), may have shown an increase in the number of whisker defects on the leads.
FIG. 1 illustrates a section of a SOP 20. Gull wing leads 12 may be formed on a body 10 of an encapsulation resin (e.g., Epoxy Mold Compound). Whisker defects 14 may form on and beneath the surfaces of the leads 12, when the leads may be electrically coated with solder. Such whisker defects 14 may not be formed when the solder is made of a tin and lead alloy, as in the conventional art. The use of only tin in the solder, without the lead component, may increase the number of whisker defects. Copper may be a primary component of the leads and tin may be a primary component of the solder. The whisker defects 14 may occur due to a nonuniform interface between the copper leads and the tin layer. An external environment change (e.g., heat treatment inducing compression stress on the nonuniform copper and/or tin layer on the surfaces of the leads 12) may cause an abnormal growth of monocrystalline tin, which may result in a whisker defect.
In addition to nonuniform copper and/or tin layers, nonuniform organic materials may also cause whisker defects 14. It may be relatively difficult to remove the whisker defects because the whisker defects 14 may continue to form about 2,000 hours to about 4,000 hours after the semiconductor package is fabricated. The whisker defects 14 may pose a problem to semiconductor packaging process because the whisker defect may cause short-circuits with adjacent leads or between electronic parts mounted on the printed circuit board, when the semiconductor package is mounted on the printed circuit board.